pith(redirected from Stem pith)
Also found in: Dictionary, Thesaurus, Medical, Legal.
pith,in botany, core of the stemstem,
supporting structure of a plant, serving also to conduct and to store food materials. The stems of herbaceous and of woody plants differ: those of herbaceous plants are usually green and pliant and are covered by a thin epidermis instead of by the bark of woody plants.
..... Click the link for more information. of most plants. Pith is composed of large, loosely packed food-storage cells. As the stem grows older the pith usually dries out, and in some it disintegrates and the stem becomes hollow. In trees the pith becomes much reduced as the woody tissue (xylem) grows. In East Asia, rice paper is made from the pith of some shrubs. Candlewicks are made of the pith of certain rushes.
The central zone of tissue of an axis in which the vascular tissue is arranged as a hollow cylinder. Pith is present in most stems and in some roots. Stems without pith rarely occur in angiosperms but are characteristic of psilopsids, lycopsids, Sphenophyllum, and some ferns. Roots of some ferns, many monocotyledons, and some dicotyledons include a pith, although most roots have xylem tissue in the center.
Pith is composed usually of parenchyma cells often arranged in longitudinal files. This arrangement results from predominantly transverse division of pith mother cells near the apical meristem. See Parenchyma, Root (botany), Stem
the central portion of a plant stem, consisting of loose parenchymatous tissue. The internal part of the pith sometimes ruptures with age, forming one large air cavity (Labiatae, Um-belliferae, some Gramineae) or several cavities (grape). Roots have no typical pith. Pith usually consists mainly of thin-walled cells, among which there may be lignified thick-walled cells (apple), latex vessels (Campanulaceae, Convulvulaceae), mucous cells (linden), or canals with volatile oils (Compositae, Umbel-liferae). The parenchymatous cells contain reserve starch, which in woody plants is concentrated mainly in external small-celled layers of the pith—the perimedullary zone. Druses or single crystals of calcium oxalate are often found in the pith.